Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271525

Area Forecast Discussion
National Weather Service Lincoln IL
1025 AM CDT SAT AUG 27 2016

Issued at 1025 AM CDT Sat Aug 27 2016

15z/10am radar imagery shows dry conditions across much of the
KILX CWA, except for a few isolated showers across portions of
Richland and Lawrence counties. With warm front now just north of
the I-74 corridor, focus for additional convection later today
will mainly be along old outflow boundaries left behind by
previous storms. Most model solutions keep central Illinois dry
through early afternoon, then show widely scattered showers and
thunderstorms developing by mid to late afternoon. HRRR suggests
the most widespread precip will be across the western half of the
CWA, primarily west of I-57. This makes sense given that is the
approximate area the early morning convection fizzled, so subtle
outflow boundaries are likely present. Have therefore gone with
chance PoPs west of I-57 this afternoon, with only slights further
east and south. Updated sky cover as well to feature more sunshine
than was previously forecast. Should be a partly sunny day with
high temperatures in the middle to upper 80s.


.SHORT TERM...(Today and tonight)
ISSUED AT 315 AM CDT Sat Aug 27 2016

The latest satellite and radar loops show a well-defined shortwave
lifting northeast through eastern Iowa and northwestern Illinois.
The wave will continue to trigger showers and storms early this
morning, with locally heavy rainfall possible due to PWAT values of
2 to 2.25". The latest HRRR actually pushes the bulk of the rain
east of our area by 16z, with little to no redevelopment through
22z/5pm. While there should be a break in the rain behind this
initial wave, the GFS/NAM/GEM/EC all point toward some redevelopment
in central IL during the day today along a trailing surface
boundary, especially east of I-55 where the theta-e ridge axis will
be focused. Those additional showers will also be fueled in part by
a warm front lifting north through IL this afternoon. Instability
and moisture content appear sufficient for that next phase of storm

Have used a mix of likely and high chance PoPs in the near term this
morning to coincide with the latest radar trends. Areas east of I-57
appear to have likely chances at some point early this afternoon, so
have confined likely PoPs to that area for now, with 30-50 percent
chances in the remainder of the area into early afternoon. Later
this afternoon, chances should begin to wane west of I-55 at least.

High temperatures today will be closely tied to the amount of
sunshine that develops between periods of rain. Yesterday, some low
90s developed south of I-70, and could see that same scenario today
after the early morning storms clear out of areas east of I-57. Have
included around 90 for LWV. Less sunshine and more periods of rain
north of I-70 should help to keep highs in the lower to mid 80s.

.LONG TERM...(Sunday through Friday)
ISSUED AT 315 AM CDT Sat Aug 27 2016

A 594 dm 500 mb subtropical ridge over the mid Atlantic states will
ridge westward toward the mid MS river valley Sunday through Tuesday
and provide very warm and humid conditions over central and
southeast IL. Highs in the mid 80s to near 90F while dewpoints of
70-75F expected during this time frame and will make for rather
uncomfortable humidity levels for a few days. Expect a daily
chance of showers and thunderstorms Sunday through Tuesday
especially during the afternoon and early evening hours with
frontal boundary nw of CWA and our area in the tropical airmass
with precipitable water values of 1.60-2.20 inches prevailing.

Upper level flow becomes nw during midweek and brings a cool front
southeast over NW IL by Tue afternoon and into southeast IL on
Wednesday and keeps at least slight chances of showers and
thunderstorm going from Tuesday night through Wed evening. Highs
in the lower 80s from I-74 north and mid 80s south of I-74 on Wed
and still rather humid with dewpoints at least around 70F.
Somewhat cooler and drier air filters into CWA on Thu/Fri with
surface high pressure over the central Great Lakes around lower MI
and bringing northeast flow into IL Wed night and Thursday and
dewpoints slipping into the lower 60s with some upper 50s from
I-74 northeast by Thu night.

Upper level ridge building back east into IL Friday night and
Saturday and keeping it dry with temperatures starting to modify.
Highs Thursday of 79-83F and back in the low to mid 80s by
Saturday. Extended models have 500 mb heights building over IL
between 588-594 dm during Labor Day weekend which would support
summerlike warmth returning.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 644 AM CDT Sat Aug 27 2016

A warm front will lift north through central IL today, with
showers and thunderstorms most numerous this morning on the tail
edge of a shortwave departing to the northeast. That wave will
continue to produce a SW to NE oriented line of storms, positioned
just west of I-55 at 12z/7am. That line will make slow progress to
the east, as individual storm cells move NE along the line. That
storm motion is producing locally heavy rainfall as storms hit
the sames areas repeatedly. IFR conditions will be possible as
that line pushes east over the terminals. PIA is just west of the
band, with the other 4 TAF sites to the east of the line of
storms. Have targeted the first half of the morning for inclusion
of thunder, as well as the late afternoon and early evening. The
late day storms will be tied to a muggy summer-time airmass in the
warm sector, with storms firing along any outflow boundaries from
this mornings storms. Storms should diminish or end by mid
evening, with clouds thinning overnight. Some patchy MVFR fog may
develop late tonight in this TAF period, with IFR/LIFR visibility
also possible.

Surface winds will become southerly as the front pushes north of
the TAF sites. It appears to have already moved past all our
terminals, based on recent wind obs. South to southwest winds
should remain between 6 to 12 kts for most of the day and this
evening, before becoming light S-SW overnight.


.ILX Watches/Warnings/Advisories...


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